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Join us as we explore the world of energy stores and transfers! In this article, we'll define different types of energy stores and explore examples from everyday life. Hold onto your seats as we dive into the depths of calculating energy transfers and unravel the mysteries of one of the most fundamental concepts in the universe. So, buckle up and get ready to embark on an exciting adventure into the world of energy stores and transfers!
Energy Stores and Transfers
Energy Transfers
"Energy transfer refers to the movement of energy from one object or system to another"
Energy can exist in various "stores" and can neither be created nor be destroyed. However, it can be converted, dispersed, or stored in different forms. Remember that energy cannot be used up.
Take an example of diesel oil in which energy is stored in the chemical bonds of diesel oil and oxygen molecules in the air. The car moves and accelerates when this energy is transferred in combustion. Although energy transfers continuously in the system, however, the net energy in the system remains constant.
Energy Stores
"Energy stores refer to the various forms or sources of energy that exist in a system or object"
A sound understanding of energy stores is crucial for comprehending various natural phenomena and their practical applications. These include but are not limited to the motion of objects, the behavior of materials, the production and consumption of energy, and the functioning of electronic devices.
Different Types of Energy Stores
Different types of energy stores are described below:
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Kinetic Energy
Kinetic energy is the energy that is associated with the motion of an object. The greater the speed or mass of the object, the greater its kinetic energy. For instance, a car moving at high speed has more kinetic energy than a car moving at a lower speed. When two objects collide or interact, kinetic energy can be transferred from one to the other.
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Thermal Energy
Thermal energy is the energy that is related to the temperature of an object or system. The higher the temperature of an object, the greater its thermal energy. Thermal energy is caused by the movement of particles in a substance, and it can be transferred through conduction, convection, or radiation. When a pan is heated on a stove, the thermal energy from the stove is transferred to the pan and then to the food inside.
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Gravitational Potential Energy
Gravitational potential energy is the energy that is stored in an object due to its position in a gravitational field. The higher an object is lifted off the ground, the greater its gravitational potential energy. When a ball is lifted to a certain height, it gains gravitational potential energy. This energy can be converted to kinetic energy when the ball is released and falls back to the ground.
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Elastic Potential Energy
Elastic potential energy is the energy that is stored in a stretched or compressed object. When an object is stretched or compressed, it gains elastic potential energy. For instance, when a rubber band is stretched, it gains elastic potential energy. This energy can be released when the object returns to its original shape.
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Chemical Energy
Chemical potential energy is the energy that is stored in the chemical bonds of molecules. During chemical reactions, the bonds between atoms are broken and new bonds are formed, releasing or absorbing chemical potential energy. For instance, when fuel is burned in an engine, the chemical potential energy stored in the fuel is converted into thermal and kinetic energy.
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Nuclear Energy
Nuclear energy is the energy that is stored in the nucleus of an atom. Nuclear reactions can release this energy, which can be harnessed for various purposes, such as generating electricity. Nuclear power plants, for instance, use nuclear reactions to produce heat, which is then used to generate electricity.
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Electrical Energy
Electrical energy is the energy that is associated with the movement of electric charges. When a current flows through a wire, electrical energy is transferred from one end to the other. Electrical energy can be converted to other forms of energy, such as thermal energy, light energy, or kinetic energy. For instance, when a light bulb is turned on, electrical energy is converted into light and thermal energy.
Examples of Energy Stores From Everyday Life
Here are some examples of energy stores from everyday life:
- Battery: A battery is an energy store that can power electronic devices, such as smartphones, laptops, and remote controls. Chemical potential energy is stored in the battery, which can be converted into electrical energy when the battery is used.
- Food: Food is an energy store that provides our bodies with the energy they need to function. The chemical potential energy stored in food molecules is released through the process of digestion and converted into thermal energy that our bodies use to maintain body temperature and carry out physical activities.
- Water: Water is a source of both potential and kinetic energy. Hydroelectric power plants use the potential energy stored in water at a high elevation to generate electricity. Waterfalls and rapids are examples of kinetic energy, which can be harnessed to generate electricity through the use of turbines.
- Elastic band: An elastic band is an example of an object that stores elastic potential energy. When stretched or compressed, the elastic band gains elastic potential energy, which can be released when the band returns to its original shape. This energy can be used to power small devices or toys, such as rubber band guns or wind-up cars.
- Fossil fuels: Fossil fuels, such as coal, oil, and natural gas, are examples of energy stores that have been formed over millions of years through the decay of organic matter. When burned, the chemical potential energy stored in fossil fuels is converted into thermal energy, which can be used for heating, cooking, and generating electricity.
Calculating Energy Transfers
Understanding the amount of energy that is transferred or stored in different systems can be quite useful. In order to calculate this energy, various equations are used depending on the specific method of energy transfer or storage being examined.
An Object Raised Above the Ground
When an object is lifted above ground level, it moves in the gravitational field of the Earth, and the energy associated with its position changes. This change in energy can be calculated using the formula for gravitational potential energy, which takes into account the mass of the object, its height above the ground, and the strength of the gravitational field.
Gravitational Potential Energy = mass x height x gravitational field strength
Example
A book of mass 0.5 kg is lifted to a height of 2.0 meters above the ground. Calculate the potential energy stored in the book.
Given:
- Mass of the book, m = 0.5 kg
- Height, h = 2.0 meters
- Gravitational field strength, g =
Potential energy (PE) = mass x gravity x height
PE = mgh
Substituting the given values, we get:
PE = 
PE = 10 J
Therefore, the potential energy stored in the book is 10 Joules (J).
For a Moving Object
A moving object possesses kinetic energy, hence we use the following formula to calculate the energy stored in it:
Kinetic Energy = 
Example
A ball with a mass of 0.2 kg. Calculate its kinetic energy if it rolls at the speed of 
.
Solution
To calculate the kinetic energy of the object, we will use the formula:
Kinetic energy (J) = 
Plugging in the values we get:
Kinetic energy = 
Kinetic energy = 40,000 J
Therefore, the kinetic energy of the object is 40,000 J.
For a Stretched Spring
A stretched spring has elastic energy stored in it which can be calculated from the formula below:
Elastic energy = 
Here: k = spring constant
e = extension of the spring
Example
A rubber band has a spring constant of 
. It is stretched elastically by 20 cm. Calculate the elastic potential energy stored in the rubber band.
Solution
The formula for elastic potential energy is:
Elastic potential energy = 
where k is the spring constant and e is the displacement from equilibrium. i.e. extension.
Here:
k = 100 N/m
e= 20 cm = 0.2 m.
Elastic potential energy = 
Therefore, the elastic potential energy stored in the rubber band is 1 J.
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